#a{
    width: 25%;
    height: 50%;
    position: absolute;
    top: 0;
    bottom: 0;
    left: 40%;
    right: 0;
    margin: auto;

    background-color: white;
    opacity: 0.7;
    border-radius: 20px;
    display: inline;
}
#b{
    width: 25%;
    height: 50%;
    left: 20%;
    top: 20%;
    background-color: white;
    position: absolute;
    opacity: 0.5;
    border-radius: 20px;
    display: inline;
}
#c{
    width: 25%;
    height: 50%;
    top: 20%;
    margin: 0 40%;
    background-color: white;
    position: absolute;
    opacity: 0.5;
    border-radius: 20px;
    display: inline;
}
#registered{
    position: relative;
    left: 15%;
    display: block;
    font-size: 8px;
}
.submit{
    margin-top: 10%;
    width: 80%;
    margin-left: 10%;
    position: relative;
}
.title{
    font-family: 华文中宋;
    text-align:center;
    padding: 10% 0;
}

#toLogin{
    display: block;
    margin-top: 5%;
    margin-left: 10%;
}